The present invention concerns a procedure and means for watching over the area in front of a lift door, of said area being formed a one-dimensional or two-dimensional image with the aid of an image-forming means based on interaction between the image points.
Endeavours have long been pursued to supplement the operation of the traditionsl photocell on a lift door by other auxiliary apparatus. It is understood that a photocell is normally able to monitor only persons passing through the door opening but not, for instance, lift passengers who are approaching the door opening. Watching over the whole door area is clearly advantageous because then the door will not close in the face of approaching lift passengers, and on the other hand the door can be closed with shorter delay than previously.
Watching over the door area can be implemented with pick-ups of various types, e.g. with ultrasound radar, Doppler radar and thermal radiation pick-ups. So far, apparatus of these types has been little employed. The reasons are to be found in the high price, considering that the means is not indispensable in view of the lift's operation, although it elevates the quality level of service. In lift applications particularly great embarrassment is also imminent if the means is excessively sensitive or if detection still persists some time after a disturbance has disappeared.